From 2247aeeeda1f474b556fdf456c98c001f3db2edb Mon Sep 17 00:00:00 2001
From: Tom Payne <twpayne@gmail.com>
Date: Wed, 15 Dec 2021 20:54:22 +0100
Subject: [PATCH 1/2] testscript: tidy up condition logic

---
 testscript/testscript.go | 39 ++++++++++++++++++---------------------
 1 file changed, 18 insertions(+), 21 deletions(-)

diff --git a/testscript/testscript.go b/testscript/testscript.go
index ea5f51e2..cf9a6724 100644
--- a/testscript/testscript.go
+++ b/testscript/testscript.go
@@ -572,32 +572,29 @@ func (ts *TestScript) applyScriptUpdates() {
 
 // condition reports whether the given condition is satisfied.
 func (ts *TestScript) condition(cond string) (bool, error) {
-	switch cond {
-	case "short":
+	switch {
+	case cond == "short":
 		return testing.Short(), nil
-	case "net":
+	case cond == "net":
 		return testenv.HasExternalNetwork(), nil
-	case "link":
+	case cond == "link":
 		return testenv.HasLink(), nil
-	case "symlink":
+	case cond == "symlink":
 		return testenv.HasSymlink(), nil
-	case runtime.GOOS, runtime.GOARCH:
-		return true, nil
+	case imports.KnownOS[cond]:
+		return cond == runtime.GOOS, nil
+	case imports.KnownArch[cond]:
+		return cond == runtime.GOARCH, nil
+	case strings.HasPrefix(cond, "exec:"):
+		prog := cond[len("exec:"):]
+		ok := execCache.Do(prog, func() interface{} {
+			_, err := execpath.Look(prog, ts.Getenv)
+			return err == nil
+		}).(bool)
+		return ok, nil
+	case ts.params.Condition != nil:
+		return ts.params.Condition(cond)
 	default:
-		if imports.KnownArch[cond] || imports.KnownOS[cond] {
-			return false, nil
-		}
-		if strings.HasPrefix(cond, "exec:") {
-			prog := cond[len("exec:"):]
-			ok := execCache.Do(prog, func() interface{} {
-				_, err := execpath.Look(prog, ts.Getenv)
-				return err == nil
-			}).(bool)
-			return ok, nil
-		}
-		if ts.params.Condition != nil {
-			return ts.params.Condition(cond)
-		}
 		ts.Fatalf("unknown condition %q", cond)
 		panic("unreachable")
 	}

From 780a119a76ad4b9a9134219257becabf9eff68d6 Mon Sep 17 00:00:00 2001
From: Tom Payne <twpayne@gmail.com>
Date: Wed, 15 Dec 2021 22:14:58 +0100
Subject: [PATCH 2/2] testscript: add build:tag condition

---
 testscript/doc.go             | 8 ++++++++
 testscript/testdata/build.txt | 9 +++++++++
 testscript/testscript.go      | 9 +++++++++
 3 files changed, 26 insertions(+)
 create mode 100644 testscript/testdata/build.txt

diff --git a/testscript/doc.go b/testscript/doc.go
index d4fe1869..d1ef5895 100644
--- a/testscript/doc.go
+++ b/testscript/doc.go
@@ -105,6 +105,14 @@ should only run when the condition is satisfied. The predefined conditions are:
  - [link] for whether the OS has hard link support
  - [symlink] for whether the OS has symbolic link support
  - [exec:prog] for whether prog is available for execution (found by exec.LookPath)
+ - [build:tag] for whether the release build tag is set; user-defined build tags
+   are not currently supported. Note that the "build:" prefix
+   distinguishes this set of conditions from the conditions recognized
+   by the gotooltest package - that package has no "build:" prefix and
+   guards based on whether the go tool supports a given tag, but the
+   "build:" tag guards based on whether the binary that's imported the
+   testscript package supports the tag.
+
 
 A condition can be negated: [!short] means to run the rest of the line
 when testing.Short() is false.
diff --git a/testscript/testdata/build.txt b/testscript/testdata/build.txt
new file mode 100644
index 00000000..b4710925
--- /dev/null
+++ b/testscript/testdata/build.txt
@@ -0,0 +1,9 @@
+[!exec:sh] skip 'sh not found in $PATH'
+
+# test that the build:tag condition works for set build tags
+[build:go1.16] exec echo ok
+stdout ok
+[build:go1.17] exec sh -c 'exit 0'
+
+# test that the build:tag condition works for unset build tags
+[build:go2] exec sh -c 'exit 1'
diff --git a/testscript/testscript.go b/testscript/testscript.go
index cf9a6724..dd309058 100644
--- a/testscript/testscript.go
+++ b/testscript/testscript.go
@@ -12,6 +12,7 @@ import (
 	"context"
 	"flag"
 	"fmt"
+	"go/build"
 	"io/ioutil"
 	"os"
 	"os/exec"
@@ -592,6 +593,14 @@ func (ts *TestScript) condition(cond string) (bool, error) {
 			return err == nil
 		}).(bool)
 		return ok, nil
+	case strings.HasPrefix(cond, "build:"):
+		tag := cond[len("build:"):]
+		for _, releaseTag := range build.Default.ReleaseTags {
+			if releaseTag == tag {
+				return true, nil
+			}
+		}
+		return false, nil
 	case ts.params.Condition != nil:
 		return ts.params.Condition(cond)
 	default: